Methods for substrate retention

ABSTRACT

Disclosed herein are methods of substrate retention properties utilizing compression features. In one embodiment a method for producing compression features comprises: assembling a mat around a substrate to form a substrate/mat sub-assembly, disposing the mat/substrate sub-assembly within a shell to form a retention assembly, and forming a compression feature on an outer surface of the retention assembly.

TECHNICAL FIELD

This disclosure generally relates to methods of substrate retention within exhaust treatment devices.

BACKGROUND

Various exhaust treatment devices have demonstrated success at reducing the gaseous emissions of internal combustion engines. Devices, such as, particulate filters, NOx adsorbers (“NOx traps”), fuel reformers, Selective Catalytic Reduction (SCR) substrates, and the like, can employ a substrate that is capable of converting emissions such as, carbon monoxide (CO), carbon dioxide (CO₂), nitrogen oxides (NOx), and the like, into less undesirable species or compounds.

Substrates are generally designed to provide a large surface area which encourages a high percentage of conversion, and can be produced in many forms, such as, but not limited to, foils, preforms, fibrous material, monoliths, porous glasses, glass sponges, foams, pellets, particles, molecular sieves, and the like. Any materials capable of withstanding elevated operating temperatures from about 600° Celsius in underfloor applications to about 1,600° Celsius in manifold mounted or close-coupled applications can be utilized to manufacture a substrate. Materials such as, but not limited to, cordierite, silicon carbides, metal oxides, and the like, have been successfully employed. Substrates can also employ catalytic metals on or within the substrate to promote conversion of the gaseous emissions.

Generally, substrates are contained within housing components, comprising an outer “shell” that can be capped on either end with funnel-shaped “end-cones” or “end-plates”, which can be connected to “snorkels” that allow for easy assembly to exhaust conduit. Housing components can be fabricated of any materials capable of withstanding the temperatures, corrosion, and wear encountered during the operation of the exhaust treatment device, such as, but not limited to, ferrous metals or ferritic stainless steels (e.g., martensitic, ferritic, and austenitic stainless materials, and the like).

Retention matting (a.k.a. mat, matting) can be utilized as a packing material concentrically disposed between the shell and the substrate to support the substrate. Matting can comprise materials such as, intumescent materials (e.g., a material that comprises vermiculite component, i.e., a component that expands upon the application of heat), non-intumescent materials (e.g., ceramic preforms, ceramic fibers, organic binders, inorganic binders, and the like), as well as combinations comprising at least one of the foregoing materials. Non-intumescent materials include materials such as those sold under the trademarks “NEXTEL” and “INTERAM 1101HT” by the “3M” Company, Minneapolis, Minn., or those sold under the trademark, “FIBERFRAX” and “CC-MAX” by the Unifrax Co., Niagara Falls, N.Y., and the like. Intumescent materials include materials sold under the trademark “INTERAM” by the “3M” Company, Minneapolis, Minn., as well as those intumescent materials which are also sold under the aforementioned “FIBERFRAX” trademark.

Using matting between the shell and the substrate offers several benefits. Firstly, matting provides insulation against heat loss through the metal shell. This is a desirable for the reason that the substrate operates at an elevated temperature (above about 500° C.) for efficient catalytic conversion. The second benefit is added impact resistance of the final device. Substrates can be produced in various designs that can comprise wall thicknesses of less than 0.005 inches, and even less than 0.003 inches, which can be brittle. Matting offers protection of the substrate against the occasional impacts encountered during use (e.g. rocks, accidents, mounting failure, and the like). Thirdly, the mat offers support of the substrate within the shell as the shell expands with heat due to the greater degree of thermal expansion of the metal shell compared to the substrate. Furthermore, as exhaust pressure increases on the upstream face of the substrate during use, a pressure gradient is created across the device that results in an axial force acting on the substrate towards the low-pressure downstream side. If the substrate is not retained properly, the device can translate move within the shell and incur damage. To curtail this possible occurrence, matting can be compressed between the shell and the substrate to provide adequate retention forces. However, compressing the mat between the shell and the substrate creates assembly difficulties that can result in misalignment and breakage of the catalyst during insertion, slower production rates, and increased cost of the components due to tight tolerancing.

Due to these manufacturing difficulties, device manufacturers desire novel manufacturing solutions that can provide adequate retention forces without these detrimental side effects. Hence, disclosed herein are methods that can provide these benefits.

BRIEF SUMMARY

Disclosed herein are methods for improving substrate retention properties utilizing compression features.

In one embodiment a method for producing compression features comprises: disposing a mat around a substrate to form a substrate/mat sub-assembly, disposing the mat/substrate sub-assembly within a shell to form a retention assembly, and forming a compression feature on an outer surface of the retention assembly.

In one embodiment, a storage medium encoded with a machine readable computer program code, said code including instructions for causing a computer to implement a method for producing an exhaust treatment device. The method can comprise: assembling a mat around a substrate to form a substrate/mat sub-assembly, disposing the mat/substrate sub-assembly within a shell to form a retention assembly, compressing a portion of the mat by forming a compression feature on an outer surface of the retention assembly, measuring a process variable, and controlling the formation of the compression feature based on the measurement of the process variable.

The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike.

FIG. 1 is a cross-sectional illustration of an exemplary exhaust treatment device 12.

FIG. 2 is an isometric illustration of an exemplary dimpled exhaust treatment device 16.

FIG. 3 is a cross-sectional illustration of an exemplary ribbed exhaust treatment device 24.

FIG. 4 is a table illustrating calculated substrate retention forces.

DETAILED DESCRIPTION

Disclosed herein are methods for generating substrate retention forces in assembled exhaust treatment devices. More specifically, methods are disclosed that are capable of attaining a desired substrate retention by forming compression features into the device's shell after the substrate/mat have been assembled therein. These compression features can create a localized area of higher density matting, which can exert higher retention forces on the device's substrate in those areas.

Disclosed herein are various references to “mat”, “matting”, and “retention matting”. Despite terminological differences, these materials are intended to be any materials that can secure a substrate within an exhaust treatment device, such as, but not limited to, intumescent materials, non-intumescent materials, and the like. Furthermore, the term “compression feature” will be referred to herein and will be interpreted as any feature that can be imparted into the shell of an exhaust treatment device utilizing metal forming techniques that compress the matting disposed within the device about the substrate. In addition, if ranges are disclosed, these are inclusive and combinable (e.g., ranges of “up to about 25 wt %, with about 5 wt % to about 20 wt % desired”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc). Furthermore, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

Referring now to FIG. 1, a cross-sectional view of an exemplary exhaust treatment device, generally designated 12, is illustrated. Exhaust treatment device 12 comprises substrate 2 disposed within shell 6 with mat 4 disposed therebetween. Shell 6 is connected to cone 8, and end-cone 8 is connected to snorkel 10. It is also envisioned that shell 6, end-cone 8, and snorkel 10 can be produced as one component, e.g., using a “spin-form” method, and/or utilizing multiple components. Furthermore, the shape of these devices can be of any design, such as, but not limited to cylinders with circular or non-circular cross-sectional geometries (e.g., oval, oblong, and the like).

Exhaust treatment device 12 can be assembled utilizing any method for producing exhaust treatment devices. More specifically, in the embodiment illustrated, it is envisioned that mat 4 is pre-assembled around substrate 2 to form a substrate/mat sub-assembly, which is then disposed within shell 6 to form a retention assembly, e.g. utilizing the stuffing assembly method.

The stuffing assembly method generally comprises pre-assembling the mat 4 around the substrate 2 and pushing, or stuffing, the substrate/mat assembly into a shell 6 through a stuffing cone. The stuffing cone serves as an assembly tool, which is basically comprises a hollow cone that can be temporarily connected to one end of shell 6. At this location, the stuffing cone can be of similar cross-sectional geometry and of equal or smaller cross-sectional area than the shell 6. Along the stuffing cone's length, in a direction away from shell 6, the cross-sectional geometry can maintain a similar cross-sectional geometry however gradually taper larger in cross-sectional area. It is through this larger end that a substrate/mat sub-assembly can be introduced and advanced. As the substrate/mat sub-assembly is advanced, the mat 4 around the substrate 2 is concentrically compressed about the substrate 2 and is eventually compressed to a point where the substrate/mat sub-assembly can be “stuffed” into shell 6.

In an alternative assembly method, known as the “clamshell” assembly method, shell 6 can comprise two halves, or “clamshells”, that can be assembled around a substrate/mat sub-assembly, compressing the substrate/mat sub-assembly therein. Once assembled, the halves can be secured together using any method, e.g. spot-welding, rolling seam welding, crimping, and the like. Furthermore, when assembled, the mating halves can be designed to also form the exhaust treatment device's end-cones 8 and snorkels 10.

Yet another method of assembly is the tourniquet assembly method. Again, the tourniquet method comprises pre-assembling a mat 4 around a substrate 2 to form a substrate/mat sub-assembly. Thereafter a steel sheet can be wrapped around the substrate/mat assembly and fastened at a seam to comprise the converter's shell. The end-cones 8 and snorkels 10 can be formed into the steel sheet, and/or attached as separated components and (e.g. welded, crimped, and the like) to form the exhaust treatment device.

Referring now to FIG. 2 an isometric view of an exemplary dimpled exhaust treatment device is illustrated and generally designated 16. In this figure, the surface of exhaust treatment device 12 comprises numerous dimples 14 that have been imparted into shell 6. The dimples 14 are disposed about shell 6 for the purpose of providing increased substrate retention. Dimples 14, can be generally referred to as “compression features” that function to compress mat 4 between the dimple 14 and the substrate 2, resulting in a localized area of higher density matting and increased retention of substrate 2.

In the exemplary embodiment illustrated in FIG. 2, it is envisioned that a punching process can be utilized to impart the multitude of dimples 14. This process can comprise a punch fabricated to a desired geometry that renders the desired impression in shell 6. The punching process can generally comprise actuating a punch to impact shell 6, which contains a mat 4 and a substrate 2, with sufficient force to impart a dimple 14 or compression feature. Although the punch is envisioned as having a configuration that generally leaves a semi-circular impression in shell 6, the punch can be configured to impart any desired impression, such as, but not limited to having a conical, spherical, cylindrical, polygonal, elliptical, or irregular shape, or the like. In some embodiments, the punching process can pierce through shell 6 to form tabs, notches, piercings, holes, and the like.

Referring now to FIG. 3, an exemplary ribbed exhaust treatment device, generally designated 24, is illustrated. In the illustration, the exhaust treatment device of FIG. 3 is depicted with multiple rib features 18 that have been formed into shell 6. The rib features 18 can be formed by any method, such as crimping. The crimping process employed can comprise; first supporting the device utilizing by any apparatus, such as, but not limited to, a support structure, frame, support arms, nest, pocket, collets, die, or the like. Second, a die (not shown) can contact shell 6 and exert a force in a direction generally designated by force vector 20. Optionally, a simultaneous compression force can be employed to the device as illustrated by compression force vector 22, which is applied on cone 8 and/or on snorkel 10, which can result in the formation of rib feature 18.

It is apparent however that although punching and crimping processes have been specifically disclosed, any method of “metal forming” can be employed to deform the shell 6 in order to form compression features that result in increased substrate retention, such as, but not limited to, punching, swaging, stamping, crimping, peening, forming, and the like. In addition, these metal forming processes can be repeated in any multiplicity, combination, and/or configuration desired, and can employ any number of metal forming operations simultaneously or in subsequent processes to produce the desired result. Moreover, these processes can also comprise process controls capable of controlling process variables for beneficial purposes such as, improved quality, improved efficiency, repeatability, and the like. For example, to ensure product quality, one or more process variables can be monitored to ensure compression features do not inflict damage to substrate 2. These process variables can be, but are not limited to, force, velocity, travel, impact depth, punch geometry, inertia, impact angle, or the like, as well as combinations comprising at least one of the forgoing and can be measured, monitored, calculated, and/or sensed utilizing process sensors, switches, meters, data recorders, transducers, probes, and the like, as well as combinations comprising at least one of the foregoing, that can be capable of producing a signal.

The metal forming methods discussed herein can also employ additional processing methods or techniques that can assist in imparting the desired compression features. Processes such as, but not limited to, annealing, heat-treating, vibration, localized heating, and the like can be employed. For example, shell 6 can be annealed prior to a stamping process that forms compression features, and can optionally undergo a subsequent heat-treating process after stamping. Another example can employ a heat source (e.g. flame, and the like) that can be applied directly to a localized area of shell 6 that can increase the malleability of the shell 6 prior to and/or during the forming process.

It is further envisioned that the operating parameters and processing variables of the metal forming processes described above can be pre-determined through engineering experiments prior to manufacturing. For example, the specific pattern, punch force, and punch depth of a punching operation can be determined prior to full-scale manufacturing implementation through a series of experiments that yield a product with the desired substrate retention.

Alternatively, or in addition, in-process measurement(s) can be employed to measure variables that can be employed in the manufacturing process (e.g., substrate retention forces, mat density, and the like, as well as combinations comprising at least one of the foregoing). For example, during assembly, another process variable (e.g., the retention force of the substrate 2) can be measured (e.g. utilizing automated methods, such as to test if the substrate 2 moves (e.g. translates)). If the measured variable (e.g., force, mat density, etc.) is below a desired value, the variable can be increased. The variable can be controlled (e.g., the force applied to the substrate in a particular area and/or across the surface of the substrate) in various fashions, such as by disposing additional compression feature(s) into the shell 6, (e.g., increasing the number of compression feature(s)), by increasing the depth of the compression feature(s), by controlling the compression feature(s)' geometry (e.g., shape, size (depth, width, etc)). Once the desired value has been attained (e.g., retention force, mat density, etc.), process of disposing the compression feature(s) into the surface of the substrate can be ceased. It is noted that the compression feature(s) can comprises a variety of geometries, sizes, and be disposed in various locations to attain a desired retention force on the substrate in the particular area. This exemplary method is intended to be non-limiting and recognized as one of many methods that can be employed to measure processing variables and operating parameters during a manufacturing process.

These methods can be embodied in the form of computer or controller implemented processes and apparatuses for practicing those processes. It can also be embodied in the form of computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium, wherein, when the computer program code is loaded into and executed by a computer or controller, the computer becomes an apparatus for practicing the method. The method may also be embodied in the form of computer program code or signal, for example, whether stored in a storage medium, loaded into and/or executed by a computer or controller, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the method. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.

Referring now to FIG. 4, a table is illustrated which reports calculated results from experiments conducted to evaluate the total increase in substrate retention forces. The materials utilized in the experiments were as follows: 1) The matting was intumescent matting with a density of 6,200 grams per square meter (g/m²); 2) The catalytic brick employed measured four-inches by six-inches (4″×6″); and 3) Dimples were modeled as the compression features on a shell 6 surface disposed in rows aligned with the axis of the cylinder, totaling 2,070 dimples at 4 millimeters (mm) in diameter each.

Three sets of calculations were figured to calculate the resulting catalyst retention forces by both the contribution of the dimples and of the non-dimpled compressed mat; the first of calculations was without dimples to determine a baseline catalyst retention force, the second set of calculations incorporated dimples at a 1 mm dimple depth, and the third set of calculations increased the dimple depth to 2 mm. For these three calculation sets, the non-dimpled and dimpled surface areas are presented, and the non-dimpled and dimpled retention forces are also presented.

In the first calculation (no dimples, dimple depth equals zero (0) millimeters, mm), the only retention force generated is by the non-dimpled surface area, which totals 9.40 Newtons (N). In the second calculation, dimples are imparted into the model at a depth equal to 1 mm, which results in a non-dimpled area retention force of 4.79 N and a dimpled area retention force of 11.04 N. Therefore, incorporating dimples with a 1 mm depth increased the total retention force to 15.83 N, which corresponds to a 68.4% increase in retention force, compared to the sample without dimples. Furthermore, it is calculated that in this experiment that dimples provides enough additional retention force so that the mat density can be decreased by 9.50%. More specifically, if the dimpled device was configured to provide the same retention force as the non-dimpled device, the mat density can be reduced from 6,200 g/m² to 5,609 g/m² to generate an equivalent retention force, hence a 9.50% decrease in mat density.

The third set of calculations dimples are imparted into the model at a depth of 2 mm. The retention force generated by the non-dimpled area of this sample is 4.79 N and the force generated by the dimpled area is 23.20 N, resulting in a total force of 27.99 N. Therefore, the additional force generated by the dimples results in a 198% increase in retention force compared to a non-dimpled sample. This increase in retention force corresponds to a 23.0% reduction in mat density to generate comparable retention force as a non-dimpled device (from 6,200 g/m² to 4,774 g/m²).

As can be seen in the experiment presented, compression features can increase retention forces and decrease manufacturing costs through the decrease of mat density.

In summary, disclosed herein are methods for substrate retention utilizing compression features that can be imparted in the shell 6 of an exhaust treatment device after a substrate 2 and a mat 4 have been disposed therein. The methods disclosed have demonstrated the capability of improving substrate retention and decreasing manufacturing costs through the reduction of matting density. This method also offers several additional benefits, such as; increased ease of assembly, decreased occurrence of misalignment/substrate damage, and lower materials cost due to the potential of wider tolerancing (e.g. shell, catalyst) and decreased mat density. Combined, these benefits can result in higher production efficiency and cost-competitiveness for the manufacturer.

While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. 

1. A method for producing an exhaust treatment device, comprising: assembling a mat around a substrate to form a substrate/mat sub-assembly; disposing the mat/substrate sub-assembly within a shell to form a retention assembly; and, compressing a portion of the mat by forming a compression feature on an outer surface of the retention assembly.
 2. The method of claim 1, further comprising; measuring a force exerted on the substrate by the compressed mat; determining if the measured force is less than a desired force; if the measured force is less than the desired force, forming subsequent compression feature(s) on the outer surface until the desired force is exerted on the substrate.
 3. The method of claim 1, further comprising; measuring a process variable; and, controlling the formation of the compression feature based on the measurement of the process variable.
 4. The method of claim 3, wherein the controlling of the formation further comprises controlling the depth of the compression feature.
 5. The method of claim 3, wherein the controlling of the formation further comprises controlling the number of the compression feature(s).
 6. The method of claim 3, wherein the controlling of the formation further comprises controlling the location of the compression features.
 7. The method of claim 3, wherein the controlling of the formation further comprises controlling the geometry of the compression features.
 8. A storage medium encoded with a machine readable computer program code, said code including instructions for causing a computer to implement a method for producing an exhaust treatment device, the method comprising: assembling a mat around a substrate to form a substrate/mat sub-assembly; disposing the mat/substrate sub-assembly within a shell to form a retention assembly; compressing a portion of the mat by forming a compression feature on an outer surface of the retention assembly; measuring a process variable; and, controlling the formation of the compression feature based on the measurement of the process variable. 